When you are sending an email to [email protected] Postfix will not check the aliases database. You need to add the postmaster user to the virtual mailbox table of anyvirtualdomaininispc3.ltd. In that case you will be able to send it as you pleased.

What you were trying was to send an email to an unknown user in virtual mailbox table of the anyvirtualdomaininispc3.ltd domain. So the message is correct. Keep in mind that the aliases database is only for local use and not for a virtual mailbox.